(1) Field of the Invention
The invention relates to the fabrication of semiconductor Integrated Circuits, and more specifically to a method of final testing of Ball Grid Array (BGA) and Chip Scale Packaging (CSP) Integrated Circuit chips.
(2) Description of the Prior Art
A Ball Grid Array (BGA) is an array of solderable balls placed on a chip carrier. The balls contact a printed circuit board in an array configuration where, after reheat, the balls connect the chip to the printed circuit board. BGA""s are known with 40, 50 and 60 mils. spacings in regular and staggered array patterns.
In order to test a BGA device, the contactor elements of the BGA device are inserted into a contactor plate having a plurality of sockets. The contactor plate is coupled to a Device Under Test (DUT) board, which is coupled to a testing machine. The DUT board is in essence a printed circuit board that completes electrical connections between the BGA contactor elements via the contactor plate and the tester. In order to test the BGA device, the tester sends signals to and receives signals from the BGA device via the electrical conductor paths provided by the contactor plate and the DUT board.
At present the final testing of semiconductor Integrated Circuits is performed using Integrated Circuit Handler apparatus whereby each of the IC packages is handled as an individual unit and is advanced to the test socket of the DUT by either gravity feed or by using pick and place methods.
U.S. Pat. No. 5,570,033 (Staab) shows a spring probe BGA contactor.
U.S. Pat. No. 5,721,496 (Farnworth et al.) discloses a method for testing unpackaged dies.
U.S. Pat. No. 5,729,896 (Dalal et al.) displays a Flip chip carrier.
U.S. Pat. No. 5,574,668 (Beaty) teaches a method for measuring BGA devices.
The present invention teaches an apparatus and method for testing integrated semiconductor circuits by means of device strip testing using probing techniques.
Using the current practice of handling integrated circuit packages on an individual basis presents problems of difficulty of handling the ever-decreasing size of the packages. Shrinking integrated circuit packages further aggravate the problems of increased tooling costs and increased lead time for test kit modifications due to the smaller IC packages and to the higher demands posed by the more accurate tolerances required for the smaller IC packages.
The present invention addresses these problems by using a new method of testing the IC packages. The need to handle IC packages on an individual basis is eliminated by using IC probing techniques applied by means of a modified probing apparatus. The individual testing of each semiconductor device will in this manner be replaced by Device Strip Testing which will be performed by the modified probing apparatus. The present invention does not require new or special tooling with the exception of the probe card which is unique for and adapted to each type of IC package. The time required to handle and test the integrated circuits will as a consequence be sharply reduced.
A plurality of individual BGA/CSP chips will be mounted on a strip, this strip will be referred to as the device strip. The device strip in turn will be mounted on an adhesive tape attached to a rigid platform (known as wafer ring) for handling of the device strip before, during and after device testing operations. This platform will be referred to as the device strip carrier. The number of BGA/CSP chips that can be mounted on one device strip is determined by the length of the device strip and by a particular package size. A device strip carrier that, for instance, can handle a device strip with a length of 8 inches (this length can be increased or decreased to fit into a 12-inch wafer frame) is referred to as a 12-inch device strip carrier.
The device strip is typically made of bismaleimide triazene (BT) substrate material. The BGA/CSP devices are strip mounted to the strip carrier using adhesive tape, this operation is a machine operation. The strip to strip carrier mount accuracy in the X and Y-directions is xc2x10.05 mm, the theta rotation accuracy is xc2x10.5 degrees.
A device strip is further subdivided into sites; each site contains a multiplicity of BGA/CSP chips or devices.
To summarize the above:
a multiplicity of BGA/CSP devices forms a site
a multiplicity of sites forms a device strip
one or more device strips may be mounted on a device strip carrier.
the device strip carrier provides the means for handling the BGA/CSP devices in the new device probing apparatus.
The new probing apparatus of the present invention has the following performance characteristics:
1) be capable of handling 12 inch device strip carriers while the probing apparatus can easily be modified to handle either larger or smaller device strip carriers
2) use cassettes that serve as the means for handling a plurality of device strip carriers in the environment of the new probing apparatus
3) use a loading/unloading arm for loading/unloading device strip carriers into and from device strip carrier cassettes
4) provide alignment of the Device Under Test (DUT)
5) be equipped with a loader/unloading transfer arm that transfers the device strip carrier from the loading/unloading arm to the device testing platform (the main chuck and heater table, see following item) and that can handle 12 inch device strip carriers and that can be easily modified to handle either larger or smaller device strip carriers
6) be equipped with a main chuck and heater table that secures the DUT during testing and that can handle 12 inch device strip carriers and that can easily be modified to handle either larger or smaller device strip carriers
7) provide two types of stepping capabilities, that is device to device within a site and site to site within a device strip.